1. Field of the Invention
The present invention relates to a phosphor and an X-ray image converter using the phosphor. More particularly, the invention relates to a complex halide phosphor prepared by activating a complex host material comprising an alkaline earth metal fluoride and an alkaline earth metal halide as the essential components (said host material hereinafter referred to simply as "complex halide") with divalent europium (Eu.sup.2+) or with divalent europium and trivalent terbium (Tb.sup.3+) and also to an X-ray image converter whose fluorescent layer comprises the complex halide phosphor.
2. Description of the Prior Art
Japanese Patent Public Disclosure No. 42,582/1974 discloses a Eu.sup.2+ activated complex halide phosphor, namely, a Eu.sup.2+ activated alkaline earth metal fluorohalide phosphor having the composition represented by the formula EQU (Ba.sub.1-x-y-p,Sr.sub.x,Ca.sub.y,Eu.sub.p)F(Cl.sub.1-a-b,Br.sub.a,I.sub.b)
Wherein x, y, p, a and b are numbers meeting the following conditions EQU y.ltoreq.0.20, x + y + p .ltoreq. 1, a + b .ltoreq. 1 and 0.001.ltoreq.p.ltoreq.0.20,
that is, a phosphor prepared by activating an alkaline earth metal fluorohalide comprising an alkaline earth metal fluoride and an alkaline earth metal halide with Eu.sup.2+. As described in Japanese Patent Public Disclosure No. 42,582/1974 and shown in FIG. 1 hereof, the Eu.sup.2+ activated alkaline earth metal fluorohalide phosphor exhibits highly efficient emission near the ultraviolet region under excitation by X-rays, ultraviolet rays or cathode ray. The phosphor is useful for X-ray intensifying screens (hereinafter referred to as "intensifying screens"), X-ray fluorescent screens (hereinafter referred to "fluorescent screens"), and X-ray image intensifier tubes (hereinafter referred to as "intensifier tubes"). In other words, it is useful as the phosphor for X-ray image converters (said intensifying screens, fluorescent screens and intensifier tubes being generally referred to as "X-ray image converters" in the specification of this invention) and as the phosphor for fluorescent lamps. Cathode ray tubes and intensifying screens employing the phosphor have been put to practical use. Recently, because of the need for increased sensitivity in X-ray image converters, there has arises a need for phosphors emitting more efficiently than the aforesaid Eu.sup.2+ activated alkaline earth metal fluorohalide phosphor.
Also, although the aforesaid Eu.sup.2+ activated alkaline earth metal fluorohalide phosphor exhibits highly efficient emission under X-ray, ultraviolet ray, and cathode ray excitation, its very long afterglow make it unsuitable for use in X-ray image converters, particularly intensifying screens. Thus, there has been an urgent need for a phosphor with improved afterglow characteristics.